Cloud storage refers to a cloud computing system taking data access and data management as the core. The system has two advantages as follows. In one aspect, the user may access to the cloud storage at any time, from anywhere, through any networkable devices, which is quite convenient to perform data access operation. In the other aspect, the user does not need to invest in a local data center or dedicated remote site to maintain and manage data, and can have a large amount of low-cost storage space by means of cloud storage. Based on the above-mentioned two advantages, the cloud storage technology has been rapidly developed in recent years, and more and more users choose to use cloud storage.
When the user uses the cloud storage, the data is usually encrypted with a key, and then uploaded to the cloud server side. However, it is difficult for the user to achieve the unconditional security of the file encryption, and there is a security risk on the cloud server side and the transmission path. In the conventional technology, the key is usually divided to increase the difficulty to crack the encryption by a malicious attacker, thereby improving the data security. For example, the user divides a key K for data encryption into N component keys based on a mathematical algorithm. The N component keys include one principal component key and N−1 component keys, and the principal component key includes information about the other component keys. Then the user sends the principal component key to the cloud storage client for storage, and sends the other component keys to different cloud storage servers for storage. In a case where the user needs the original key K to decrypt the data, the user obtains the component keys on the cloud storage servers, and may recover the original key K with the component keys in combination with the principal component key.
However, in the method of dividing the key, the principal component key sent to the cloud storage client and the component key sent to the cloud storage server may be easily intercepted by a malicious attacker during transmission. Further, the above-mentioned method is based on the mathematical algorithm, and the progress of mathematics and rapid development of computer technology will give rise to the cracking of the key K for data encryption, and eventually lead to serious data security issues for cloud storage.